Telephone system



July 9, 1940. J. w. M CLEW ET AL 7,633

TELEPHONE SYSTEM Filed Sept. 12, 1938 ll Sheets-Sheet l ill INVENTORS JOHN WILLIAM MCCLEW OW AVIS PEARCE 4 i Z M ATTORNEY y 1940- J. w. McCLEW El AL 2, 7,633

' TELEPHONE SYSTEM Filed Sept. 12, 1938 ll ShetS-Sheet 2 rbl SW4 2 L5 I 48 E 2 INVENTORS JOHN WILLIAM McfiLEW OWEN PEARCE w ATTORfiEf July 9, 1940. J. w. M cLEw ET AL I 2,207,633

TELEPHONE SYSTEM Filed Sept. 12, 1938 ll Sheets-Sheet 5 2425252950 31 -32 3a\ mVENToRS JOHN WlLLlRM McCLEW BY 0 AVIS PEARCE ATTORN E July 9, 1940. J. W. MQCLEW El AL TELEPHONE SYSTEM Filed Sept. 12, 1938 ll Sheets-Sheet 4 INVENTORS JOHN WILLIAM McCLEW BY wen AVIS PEARCE ATTORNEi July 9, 1940. J. w. MQCLEW ET AL 7,633

TELEPHONE SYSTEM Filed Sept. 12, 1938 11 Sheets-Sheet 5 mvswrons JOHN WILLIAM McCLEW O N AVIS PEARCE ATTORNEY July 9, 1940. J. w. M cLEw El AL 2,207,533

TELEPHONE SYSTEM Filed Sept. 12, 1938 11 Sheets-Sheet'G INVENTORS JOHN WILLIAM McCLEW BY ow? AVII5 PEARCE ATTzmws July 9, 1940. J. w. M cLEw ET AL TELEPHONE SYSTEM Filed Sept. 12, 1938 11 Sheets-Sheet 7 INVENTORS JOHN WILLIAM McCLEW ow ms PEARCE ATTORNEY.

July 9, 1940.

J. W. M CLEW ET AL TELEPHONE SYSTEM Filed Sept. 12, 1938 11 Sheets-Sheet 8 BY g z INVENTORS JOHN W LLIAM MC CLEW AVIS PEARCE ATTORNEY July 9, 1940. J. w. M cLEw El AL 2,207,633

TELEPHQNE SYSTEM.

Filed Sept. 12 1938 ll Sheets-Sheet 9 INVENTORS JOHN WILLIAM Mc CLEW OWEN AVIS PER BY RCE i a ATTORNE July 9, 1940. v I J. w. M cLEw El AL 2,207,633

TELEPHONE SYSTEM Filed sept. 12, 1958 11 Sheets-Sheet 10 INVENTORS JOHN WILLIAM McCLEW BY OWEZWI 5 PERRCE y 1940. J. w. M cLEw ET AL 2,207,633

TELEPHONE SYSTEM Filed Sept. 12, 1938 ll Sheets-Sheet l1 4 I 751. fll+ -|b T3 INVENTORS JOHN WILLIAM MGCLEW ATTORNEY Patented July 9, 1940 2,207,633 a nns-PHONE sYs'r'EM John Wi lliam McClew, Liverpool, and Owen Avis Pearce Barnston, England, assignors to Associated Telephone &Telegraph Company,

- GhicagoyllL, a' corporation of Delaware Application September 12, 1938, Serial No. 229,502'

- In Great Britain September l7, 1937.

7 The present invention relates to telephone Sys tems and is more particularly applicable to'semiautomatic telephone systems such as are-used in rural areas. In such areas the telephone exchanges involvedmay include a main exchange,

a few satellite exchanges and numeroussmall exchanges of the semi-automatic remotely-controlled type which will hereafter be referred to as R. C. -X.s Atypical layout for such an area is lo described in the application of C. E'. Beale, I. T. Richards and'O, A. Pearce, Serial No. 230,416, filed'S'ept. 17,1938, in which one radiating branch from the main exchange is assumed to include a" tandem satellite exchange, a tandem R1 C. and a terminal R; C. X. f Y 1 j g The arrangement is that the subscribers on the main exchange and tandem satellite exchange are provided with dial telephones and'are permitted to set up calls to other subscriberson their own exchange automatically, butforall external calls the subscribers must dial a distinctive digit which routes the connection to the manual board at the main exchange, from which the operator controls automatic switches in the one or more exchanges involved in routing the call to its required destination.

The subscribers on the tandemandterminal R. C. X.s are notprovided with fdial telephones and on all calls they must signal the operator,

at the manual board who after ascertaining the 7 number of the wanted party controls automatic switches to set up the connection automatically. In case the wanted party is connected to an exchange on thesame radiating-branch from the main exchange as that over which the call was originated, the operator must be enabled to dial back over the junction route takenfintouse by the calling party so as to gain accessto any of the exchanges connected thereto, the apparatus taken into use at the originating exchange by the calling party having to be held during this time. After the setting up of the connection to the wanted party, the operator withdraws her plug and the two subscribers are then" either linked together locally in the originating exchange in the case of a call for a local subscriber or alternatively they are linked together over the junction or junctions connecting the two subscribers exchanges together. I 50 The general object of the invention isto provide improved signalling and line testing facilities in areas of the above type, use being made of high voltage responding devices'employing gas discharge tubes.

' In the above circumstances difficulties arise wherefor'example it is desired to perform from the main'exchange a faultroutin'e test on the subscribers lines of the exchanges connecting therewith since only the ordinary selector train can be utilised. It is unlikely'that it would ever bean economical proposition to provide special.v

testing junctions and switchesfor this purpose and it is; one object of the invention to provide arrangements whereby normal service junctions can be utilised for the setting up of line test connections.

According to one feature of theinvention in a telephone system including a plurality of exchanges and having calls fora party connected to one exchange set up over automatic switches within that exchange from an operators position located in another exchange to which a calling party is automatically connected, in order to per-} mit testing of a subscribers line to be carried out over a connection set up from the exchange in which the operators position is located a relay connected to'the line in series with a gas discharge tube is adapted to be operated in response to a pulse of high voltage and thereupon to cut out the feeding bridges and transmission condensers and give a metallic loop.

11; will be understood that an arrangement a this type is associated with each transmission bridg'ein the connection extending between the test desk and the desired line and according to another feature of the invention, in a telephone system including a plurality of exchanges connected'i'n tandem and arranged for signals to be transmitted by the connection of a high voltage to the line, a signal causes the operation of a relay connected in series with a gas discharge tube, the operation of: the relay serving to cut out the feeding bridges and transmission condensers so that the high voltage signal is extended to a succeeding exchange to effect a switching operation thereat,

Furthermore it is usually arranged that when an R. C. X. subscriber originates a call he gives to the main exchange operator both his own numher for fee "allocation purposes. and the wanted partys number. It is desirable however to provide arrangements whereby the main exchange operator can verify the number given by the calling party-in order to prevent fraud particularly where a long distance call is required. This is conveniently effected by setting up a checking connection back over the junction utilised by the calling party has given his correct number, particularly if only one junction is provided, or alternatively if the operator desires'a more definite check she may cut-in on the engaged line and ask the number of the subscriber. It is now necessary to release the checking connection set I up at the R. C. X. whether the call is to be set up locally or extended to a'distant exchange and it is another object-of the invention to provide improved arrangements whereby this may be simply effected, it being realised that ordinary direct current signalling arrangements cannot readily be adopted since they are already utilised for other purposes.

I A further feature of the invention is that both the above mentioned facilities are provided in that in a telephone system including a plurality of exchanges cannected in tandem toan exchange provided with an operators position, a high voltage signal transmitted from the exchange in which the operators position is located is arranged according to its polarity to operate a relay connected in series with a gas discharge tube to effect either the cutting out of feeding bridges. and transmission condensers or the release of a connection in any of the tandem connected ex changes.

According to another feature of the invention in a telephone system including a plurality of exchanges at one-of which an operators position is located, calls from the other exchanges are automatically extended to the operators position whence a connection is set up to the number given by the calling party as his own, the numerical switches in the originating exchange which are set to complete this verifying connection being subsequently released in response to the transmission of a high voltage pulse to effect the operation of a relay connected to the line in series with a gas discharge tube whereby the same numerical switches may be used for setting up the wanted-connection without the original connection to the operator being released.

The invention will be better understood from the following description of one method of carrying it into efiect, reference being had to the accompanying drawings comprising Figs. 1-11 which should be arranged in the manner shown in Fig. 12 to form a complete-circuit diagram. This shows an R. C. X. board having tandem facilities and with provision for one incoming main exchange junction and for up to ten lines which include local lines and also a line to an adjacent R. C. X. if the board is functioning in a tandem capacity. One link circuit employing a 12-point line finder switch of the reverse drive uniselector type and a similar connector switch is provided and in addition a further half link circuit having theconnector portion only is provided. Although the switches are of the 12-point type, position I is utilised as the home position and position i2 is not used, the remaining ten positions, to which the connector switch can be set by the dialling of a single digit, serving ordinary subscribers,coin box subscriberaparty line groups of subscribers (one set of contacts being allotted to each party line) and one outgoing junction to an adjacent R. C. X. It will be understood that the board at the adjacent R. C. X. may be similar to that shown except that it is not wired for tandem facilities.

Before proceeding with the general circuit description of the board, it will be convenient to consider the operation of the all-relay ringing current and tone generating equipment of Fig. 1-1. that ringing current and tone may be required, earth is applied to the common ringing start lead l3 whereupon relays RC and RT operate .in series. The former at armature rtl inserts its upper winding in series with the lower winding and since the two windings are arranged in opposition to one another, relay RT then releases. .Thereupon the cycle of operation is repeated as long as the earth is maintained on the lead [3 When the equipment is taken into use so thereby producing a tone of definite frequency in the transformer T2. At armature ml the vibrator RV is set into operation and produces an alternating current for ringing purposes in the left-hand winding of the transformer T3 in wellknown manner. nected to relay IR which is shunted by the high capacity electrolytic condenser QG.' This relay operates inseries with resistance YO after a delay represented by the charging up time of the'condenser, and at armature z'rl operates its relief relay IRA. At armature z'r2 the low resistance YP is bridged across the winding ofrelay IR and condenser QG so that relay IR releases and the condenser is discharged. Relay IR on releasing again connects up the condenser charging 'circuit and releases relay; IRA and the cycle of operations is now repeated. By this means relay IRA is pulsed at a definite slow rate so as to pro' vide an interrupted ringing current supply. to common lead 16 and an interrupted ringing current supply to common lead l2 by way of arma tures iral and 'ira'2 respectively.

When busy tone is required, earthis applied to common lead It whereupon relay BZ is energised and de-energised at a predetermined rate in series with the impedance BC in the same man- At armature r02 earth is conner as relay RT is operated in. series with relay RC so that a tone at a frequency corresponding to the usual busy tone isproduced in transformer T1.

The start earth over common lead l0. also extends to relay XB which is slow to operate and. 7

release and on operating energises relay .ZB

which is also slow to operate and release; .This

relay in turn at armature zbl short-circuits relay XB which therefore releases and in turn shortcircuits and releases relay ZB. .The two relays thus interact and at armature am the busy tone supply to common lead I I is interrupted to give the usual well-known busy indication.

A ringing return battery is connected to come mon lead [5 while the lamp RR inserted in the continuous ringing current lead 11 serves to limit the current flow taken from thegeneratorto" a value suitable for application to the junction.

925 The fusealarm relay FA connects over lead 14 with the fuse alarm. bar and is therefore operated if a fuse blows. It then lights the fuse alarm lamp FAL'and operates thev alarm bell AB, facilities being'provided to out these out of circuit if so required by means of the keyKAC. Relays line according to whether the telephone instrument is of the magneto or the central battery type'. In the former case as the line relay R .is to respond to alternating current, it is connected across the line by way of the condenser QA,.while in the latter case the condenser and the dotted connections are omitted and the battery and earth connections shown by lines intercepted by circles are provided. In either case relay R is operated and locks over its right-hand winding over lead 20 in series with the common finder start relay FS, assuming that the link circuit is disengaged. Relay FS thereupon at its armatures jsl and T82, Figs. 1 and 2, completes testing and hunting circuits for the line finder switch which is set in operation to huntfor and con-' nect with the calling line.

Testing is now made for battery potential which marks the calling line and if the wipers of the switch are not standing on the calling line, the test wiper LFI will not encounter a battery potential so that relay GFwill operate in series with the upper winding of relay FF, the winding of relay GF being of high resistance so that relay FF will not operate in this condition. Relay GF at armature gfl 'energises the magnet LFM which thereupon opens its interrupter contacts fm and releases relay GF so that the magnet is now deenergised and in so doing advances the wipers to the next set of contacts. The magnet LFM and relay GF continue to interact and advance the wipers step by step until the contacts associated with the calling line are reached when wiper LFI will encounter battery potential by way of armature 1'2 and the cut-oil relay K and resistance YA in parallel. Under this condition relay GF is shunted and cannot re-operate but relay FF operates over its two windings in series and at its armature fil applies guarding potential by way of its low resistance lower winding to wiper LFI, this circuit serving to hold relay FF operated and also to operate the callingsub scribers cut-off relay K. A circuit is now completed over armatures brl andbal, Fig. '7, lead 2| and armatures fs3 andrbl to operate the slowto release relay RA and this relay in turn operates relay RB. Relay RB thereupon at armature rbl locks and disconnects relay RA and during the operated period of relay RA the callingsignal is repeated in the form of a pulse of ringing current over the junction extending" to the main exchange to signal the operator at the manual board. Ringing current is transmitted from common lead I! by way of armature m2 'to the positive junction conductor, the ringingcurrent generator having been started up on the operation of relay FS when earth was applied over armatures fsfi and bat! to the common ringing start lead I3.

In the area described in the previously mentioned specification, this tandem R. C. X. board is connected to the main exchange by way of a so-called tandem satellite exchange and accord ingly it will be understood that the ringing pulse is received at the tandem satellite exchange and is repeated from there to the main exchange after having brought about theselection of a free junction from the tandem satellite to the main exchange.

Returning again to the operation, of the relays FF and K on the finding of the calling line; relay K at armatures kl and k2 disconnects relay R from across the line conductors, at armature k3 opens the start circuit and at armature k4 locks up and disconnects resistance YA from across its own winding, the purpose of this resistance being to increase the operating speed of relay FF so that the driving circuit may be efficiently broken'when the calling line is reached. Relay FF at armature ffl disconnects relay GF and at armatures 32-176 connects the wipers of the finder switch through to, the link circuit. At armature 171, Fig. 6, the finder start relay FS is disconnected from the start lead 20 but it is maintained energised over armatures Th2 and ,fs4. The busy tone relay ET is connected to the start lead in its place so that if any other subscriber calls while the link is engaged, this relay will be operated in series withthe calling line relay and at armature bti applies earth to the common busy tone earthed so that in the present instance relay RS is operated and at its armatures sl, T32 and 183,

Fig. 2, connects battery feed by way of the windings of relay FI across the calling subscriber's loop. Relay FI now operates and prepares a operating circuit for relay DD, Fig. 3.

When the operator plugs into the calling junction relay A, Fig. '7, is operated over its upper winding in series with the differential relay 0C, and at armature 0.2, Fig. 3, operates relay B. Relay B at armature b2 operates relay BA and at armature 03, Fig. 6, extends the lower junction lead through to relay A, this relay now remaining held over its two windings in series. The battery potential via resistance YJ is disconnected from the negative conductor at the same armature, this circuit normally serving for the purpose of charging the R; C. X. battery from the main exchange. The differential relay OC which may have momentarily operated over its upper winding on the initial operation of relay A now releases and its operation produces no undesired to the fact that the link is engaged. He receives busy tone in these circumstances as previously mentioned and will then hang up his receiver. Since however his line relay'R remains locked up'when the link becomes free the call is automatically extended to the operator. In this case however, relay FI will not be operated and this will be indicated by the absenceof the reverse battery supervision given by the operation of relay DR. The operator will now ring the calling subscriber by operating a key which extends an unbalance signal over the junction, for example by the connection of earth potential to both the negative and positive conductors, whereupon the differential relay OC operates in series with relay A which remains energised. Relay 0C thereupon at armature 00!, Fig. 3, earths lead 35 and so operates the slow-to-operate relay RF, Fig. 5, which at armature rfl applies earth to the ringing start lead l3, and at armatures If! and 173, Fig. 1, extends ringing current from common lead .I I over the line finder wipers to the calling line.

Theoperator converses with the calling party and takes particulars of the call required and requests the calling partys number in addition to the wantedpartys number in case it is required to record a fee against him.

If this is so, the operator may wish to verify the correctness of the number which the calling party'has given as his own, andshe accordingly dials-back over. thejunction into the link cirerator is received on relay Aand on each release 5 of this relay earth is extended over armatures 1212,01, 002 and hi to relay C and in parallel therewith over armatures k4, byl and M3 to the connector switch magnet CSM. The wipers of this switch are accordingly set on to the calling line, relays B and C holding operated during the impulse train due to their slugs.

At the end of the train, relay B remains held while relay C releases after its slow release period. Since the line to which the wipers have been set is an ordinary local one as distinct from a party line or line from an adjacent R. C. X., the particular conditions required in the link circuit are set up by providing a strapping connection from the relevant contact on the CS5 bank, Fig. 4, to terminal LOC so that relay CR is operated on the release of relay C at the end of the train. Relay CR thereupon at armature 0T4, Fig. 3, prepares a circuit for relay DD for the supervision of the called party, the original operating circuit for this relay having been disconnected at armature 0115 on the operation of the connector switch off-normal relay VN over wiper CS6 (Fig. 4) when the connector switch is stepped off-normal. Relay DD however holds operated over armatures c3 and ddl until the end of the dialled impulse train. Relay ID, Fig. 4, which was operated by relay BA is also held during the. train and at its armature idl, Fig. 2, short-circuits armature a! to prevent it from giving a succession of clicks to the calling party.

"Since the line to which the connector wipers havebeen set will be engaged, the operator will now receive a busy tone. Relay C at armature 02 operates the slow-to-release relay E and at the end of the train these two relays release in sequence, and While relay E remains up a circuit is completed over armatures c4 and 05 for relay If this relay fails to operate due to the called line being busy, on the release of relay E a circuit' is completed over bank and wiper CS6, Fig. 4 and armatures ba5, e2, h5 and M8 to operate relay BY. Relay BY at armature b114, Fig. 3, connec'ts up the busy tone lead I I via lead 30, armature ca l and lead 39 to the upper winding of relay A from whence the tone is induced in the other two windings and applied in a balanced circuit to the incoming junction and so to the operator.

If the operator Wishes to check the number further, she may now operate a trunk offering key which unbalances the lines to bring in again the differential relay 0C. Since the connector has been set, that is to say relay BN is operated, the operation of armature ocl now extends an earth by way of armature ccl, lead 35 and armaare 0714 to operate relay RC. Relay RC completes a circuit from earth, armature ba l, Fig. 4, lead 36, armatures haZ, 1'03 and bp2 to operate relay HR over its left-hand winding and this relay at armatures M3 and hr l Fig. 4 connects the operator through to the busy line, the connection to the same party over the finder side of the bank being opened at armatures m5 and m8. Relay HR also at armature hr8 releases relay BY whereupon busy tone is removed and relay HR is enabled to lock up over its right-hand winding.

After having spoken to the subscriber and verified that he is actually the calling party, the operator must clear down the connector half of the link and this she does by throwing her identification release key which has the effect of applying a high voltage pulse to the junction which causes the neon tube NL to strike, the polarity of the pulse being such that current fiows'gin'a direction for which rectifier MRB is conductive, and hence relay TO operates. Relay T0 at armature tol, Fig. '7 completes a circuit over armature 785 to operate relay BR which at armature brl locks up in series with relay FS dependent upon armature zmfi and at armature 2112 Fig. 3, releases relays B and BA in turn, whereupon at armatures 1M3 and bafi homing circuits are completed for the connector switch in conjunction with the interacting relay GC'. Relays CR and HR which are held operated dependent on relay BA are also restored to normal. Relay BR re,- leases when the switch reaches normal or when the operator releases the key if it is still operated at this time andrelays B and BA then again operate.

Assuming that the required party is also a local subscriber, the operator now proceeds to dial his number thereby positioning the connector Wipers on his line which is given an immediate ring followed by intermittent ringing. Considering the operations during the impulse train, relays B, BA and C are held operated, while relay VN is again operated as soon as the. con nector switch moves off-normal. Relay C at ar mature 02 operates relay E which in turn operates relay ER. At the end of the impulse trainrelay C releases as already described and disconnects relay E, earth now being extended from armature ba l, Fig. 4, lead 36, by way of armatures b112, e4 and 05 through the windings of the switching relay H in series and armature pm! to the test wiper CS3.

If the calling party is disengaged, battery potential by way of the winding of. his cut-01f relay K will be encountered so that relay operate. Relay I-I thereupon at armature"hl short-circuits its right-hand winding and so applies low resistance earth to the test Wiper for guarding purposes. At armatures 71.6 and h'l, Fig.

4, a circuit is completed *for ringing the wanted partys bell and it will be seen that as' long as relay ER remains operated, continuous ringing will extend by way of common lead ll, armature er! and the upper winding of the ring trip relay F to the negative line, a return path being found over the positive line to the ring return battery by way of resistance YE. and common'lead 151 The wanted subscriber thus receives an immedi ate ring and on the release of relay ER following that of relay E the interrupted ringing leady lfi is connected up in place of the continuous ringing lead H.

tripped by the operation of relay F'Which at its right armature f l removes the short-circuit from H mu Relay DD was again operated on the re-energisation'of relay BA but is released on its lower winding over which it operates fully in series with resistance YF to earth by way of armatures rel, c112 and but. the operators circuit through to the wanted party at armatures f2 and f3, Fig. 4, a battery feed to this party being connected up from earth over Relay F extends armature hsrZ, Fig. 3, upper winding of relay CI,

lead 26, armatures f1, 1W8, hsr l, c'b'l, al,-sw5, 0112,

012, f3 and 716 to the positive connector wiper CS2 and from battery via resistance YD, Fig.3, armature hsr3, lower winding of relay CI, armature swl, lead 28, armatures hr -l, f2 and h! to the negative wiper CSl. Relay CI thereupon op erates and at its armature cz'l completes a cir-v cuit over armature 014 to re-operate relay DD which in turn operates relay; DR, Fig. 4, to give supervision to the operator that the called party is. on the line. The two subscribers are nowconnect'ed via the link circuit, battery feeds being supplied to the calling and called. parties by relays FI and CIrespectively. The operator with- ,draws from theconnection by removing her plug, whereupon relay A releases and in. turn releases relay B. Relay BA however remains held from earth over armatures h3, ,fi3 and be! and so maintains holding circuits for relays FS, H, F and CR. Release of the linkcircuit is thus under control of the calling party and when he subsequently hangs up, relay F1 releases and releases relay BA which in turn releases all the various relays operated and brings about the homing of the connector switch in the manner already described. If thewanted party'is busy relay BY is operated as in-the case of .the verification connectlon and busy tone is returned to the operator. She will then inform the calling party who will replace his receiver thus. releasing relay F1. The operator will then remove. her plug to permit relays A, B and BA to fall away so that elase take place in the usual manner. I

In case the callis intendedfor a party line on the same exchange, the wipersof the connector are set by the digit dialled to a-distinctive position where relay PR, Fig- 4, is-operated onthe release of relay C over the CSS'Wiper and bank and cross-connection to terminal PL. Relay PR upon operating at armature 'pr' l locks upto'earth at armature ba4, at armature prl operates relay CR and at armature m6 removes the shorti circuit from the lower winding of the ring, trip relay F, armature er2 being operated at thistime' pletes a circuit for repeating the'succeeding digit in the form of earth impulses over the positive connector wiper and bank CS2 so as to cause equipment associated with the party line to bring about the selection of the required party. This a circuit extends from earth, armature e113, Fig. 2, armatures pr8, hsr4, cbl, al $105, 0122, 01-2, f3 and mi to the positive wiper CS2 and thence to the party line equipment. Relay A in responding to the next digit selects the required party'on-the party line, the impulses being repeated by arma- During this impulse train relay RC isture al. operated over armatures c4 and e112 and at armature rcZ opens the circuit of relay ED whichhowever remains held until the end of the train.

When relay E releases,the circuit of relay F is opened at armature c3 and it de-energises to initiate the ringing operation. Relay RC is at Y OGJ. Relay HS is accordingly operated on the release of relay C and at armature hsl locks itself up and operates relay HSR which at armatu-re hsrl lower winding of relay RelayF operates and thereupon a loop is completed across the outremoves the short-circuit from the going conductors to the adjacent R. C. X. to .pre';

pare the distant equipment to respond to further digits dialled by theoperator. This loop extends as, follows: negativeconnector wiper CSl, armatures h'l, f2 and M4, conductor 28, armature sw], lower winding of relay CI, armature hsr3, lower winding of shunt field relay CD, upper winding of relay CI, conductor 26, armatures hsr l, cbl',

al, sw5, cbZ, cr2, hsr5, j3-and 71.6 to the positive connector wiper CS2.

When the operator dials the next digit, relay A responds in the usual manner and at armature a! repeats theimpulses forward to the adjacent R.'C. X. During each impulse train relays C, E and ER are operated and. hold in the usual manher and at armature e5, Fig. 3, relays CIand CD are short-circuited soas' to give an impedancefree impulse repeating loop. At the end of the impulse train when relays C',IE and ER restore, relays CI and CD are again bridged acrossthe line for supervision purposes from the distant R. C. X. When the wanted subscriber answers,

battery is reversed back over the junction in'the usual manner to bring about the operation of relay CD which at armature cdl operates relay DD which thereupon operates relay DR to give the required supervision to the operator and also at armature ddZ short circuits the impulse confrom a partyline subscriberto another party on tact toprevent the connection to the adjacent the same line, a callingsignal is given to the manual board as before and the line finder hunts to locate the callihgpartys line. It should be explained that contacts in theline' finder bank LE5 which represent'party lines are cross-con nected to corresponding contacts in theconneotor bank CS4, Fig. 5. Consequently since thefsubj-f scriber required is on the same party line 'as the calling subscriber, when the operator-dials back over the junction and sets theconnector half-of the link into engagement with the same line as is calling, relay PRR, Fig.1 is operated by way of armature H5, bank and wiper LF5,-cross connection to CS4 bank and wiper, armature m3 to earth, relay PR, Fig. 4, being operated since the Y connector switch CS to set onto a party line.

The operation of relay PRR at its armature pi rl j 5, brings about the operation oi relay H over" itsright hand winding on the release of relay;'-C- regardless of the factthat the selected line tests busy so that the operator is connected directly to the busy line.v A further digit is now dialled:

which is repeated from the link 'circuitin the form of impulses into the selected party line equipment in the manner already described and thus causes the wantedpartly to be connected in parallel with the calling party. On a revertive' call the calling party line subscriber'is instructed to hang up after giving particulars of the wanted party to the operator so that when the operator: completes the'dialling operation and-ringing current is applied to theparty line, both calling and called parties"bells are rung. When the called party answers, ringing is tripped thereby indicat ing to the calling party that the callhas been answered'whereupon he also removes his' re'-' R. C. X. is released, the link taken into use being maintained throughout conversation.

Consider now the case in which a call is originated in the adjacent R. C. X. which is connected to the main exchange by the tandem R. C. X. in which the equipment shown is located. The line relay R will be operated over the junction from the adjacent R. C. X. whereupon the main exchange operator will be signalled in the usual manner; and a finder switch will be caused to hunt for the calling junction which appears in its banks in the same way as a subscribers line. On the completion of the finding operation, the connection is switched through and the operator takes particulars of the calling and wanted parties numbers. She may now if she desires set up a verification connection and for this purpose will dial the number of the calling party which will result in impulses being transmitted back over the junction to the adjacent R. C. X. v I

The contact in the bank LFE corresponding to the junction is wired to terminal J, Fig. 4,

and consequently when the finder comletes its operation relay HS is operated but not relay HSR as it is now short circuited.

The operator first dials the digit corresponding to the adjacent R. C. X. and the connector wipers are set accordingly and encounter a busy condition but tone is not transmitted back owing to the operation of armature hs l. Relay ID is now released so as to render the impulsing armature al effective and the succeeding train of impulses is repeated over the junction to operate the connector portion .of the link in the R. C. X. The impulse repeating circuit extends as follows: negative line, Fig. 1, bankand Wiper LF3, armatures 172, 1'54 and sum, upper winding of relay FI, armature rsl, winding or polarised relay FD, lower winding of-relay FI, and armatures r83, T3, hsrfi, cbl, al, sw5, 0122, 012, hsr and 173, wiper and bank LFZ to the positive line. The relays FI and FD are short-circuited during dial:

ling by the low resistance Y0 and armature era in the usual manner to give an impedance-free loop.

If the number has been correctly given,. the operator will receive a busy signal. This in the circumstances is considered a sufficient check and provision is not made for the operator to out in on the line. 1

To release the verification connection set up at the adjacent R. C. X., the operator operates relay TO by extending a high voltage signal as already described, but this time since relay RS will be unoperated owing to the fact that a junction has initiated the call at the tandem R. C. X., relay T0 at armature to l operates relay SRA instead of relay BR. Relay SRA at armatures sra! and sraZ completes a metallic connection from the main exchange junction through to the calling R. C. X. junction and so extends the high voltage signal through to the calling R. C.

to bring about the necessary release. During this time delay A is disconnected from the line and.- a local holding loop is provided over armature sra3'and resistance YK, while at armature sra4, Fig. 2, relays FI and FD are disconnected from the line. At the conclusion of the pulse relays TO and SRA restore and the operator may now set up a connection to the wanted party by dialling his number in the adjacent R. C. X.

When the wanted party answers, the polarised relay FD is operated as a result of the-reversal of current over the calling. junction in the usual I manner and operates relay DD, Fig.3, whichiiii turnoperates relayDR,-Fig..4 to give supervision to the operator. The operator now withdraws from the connection and frees the junction to the tandem R. C. X., whereupon relay A restores and opens the loopacross the junction to the calling adjacent R. C. X. so that this junction is also freed and the two subscribers on the call ing adjacent R. C. X. are therefore-linked together locally; The release of relay A also re-' 1 stores the equipment of the tandem R. C. X.-board to normal, relay BA not being held in this case over armatures 7L3 and fi3.

In the case of an incoming call from the main exchange to the R. C. X. the operator takes into use the main exchange junction. and dials the required number and the connector half of the link establishes connection with the wanted party who is rung .in the usual manner. In case, how-. ever, he should be busy, the operator will receive the usual busy signal owing to thebperation of relay BY and if the incoming call is for example a long distance call, the operator may wish to cut-in on the busy connection and offer it This she does by operating her trunk offering key which unbalances the line and brings about the operation of relay OCand in turn relays RC and HR, Fig. 5- asbefore. On the release of relay 0C when the operator restores her key, relay RC also releases but relay HR remains locked over its right-hand winding and armature M1, and hence relay B1? is now operated from earth by way of armature bad, lead 36, armatures ha2, T03 and i212, winding of relay BP to battery. Relay BP'at its armature bpSfleXtendS earth from lead 36 over armatures byZ, 17123 and cite the windings of relay H in readiness for the subsequent operation of this relay. If the incoming call is accepted, the subscribers in conversationare asked to restore their receivers. The operator again depresses hertrunk offering key which again operates relay OC and in turnrelay RC and this time the operation of relay RC extends earth over armatures r03, b102, rsfi, 011.3,

1015 and in! to thetest wiper CS3 to bring about forced release of theexisting connectionin case the unwanted'party should attempt to hold itby not hanking up. At the end of-the pulse relays 0C andRC release and relay H now operates over its two windings in series to the wanted partys cut- 01T relay and this party'is now rung in the normal manner via the ring trip relay F. r

In case the call had been extended to an ad-.

jacent exchange, relay 00 upon operating as a result of the unbalancing of the lines would have operated relays RC and HR as before and since. in these circumstances relay HS would be op--- erated, the unbalance signal would be repeated.

by way'of armatures T04, 1132 and 7113 over the junction to the adjacent exchange to bring about cut-into the engaged line. It will be seen that on a call of this nature, since relay BA. is oper ated without the operation of relay FS, relay" OE is operated'over armatures bail and is! and at armature 06! connects up relay BT toflb'u'sy the link to calling parties.

Furtherconsideration will now be given to the conditions when two subscribers arein conversa-" tion on aqcall local to the tandem R. vC. X; or between a tandem R. C. X. subscriber. and-an adjacent R. C; X. Subscriber and the" operator withdraws her plug. Relay A then: releases and; in turn releases relay B and relay;BA remains held over operated armatures h3,.fi3 and betas.

previously described. A circuit is now completed for relays CA, CB and CC in seriesfrom earth via armatures b2 and M2. These relays upon operating switch the incoming junction over to the additional half link circuit which comprises a connector portion only so that a further incoming main exchange call may be completed even though the ordinary link is engaged. The actual switching over of the junction is accomplished by the armatures cal -ca4, Fig. 8, while armatures of relays CB and CC switch over the impulsing and other circuits in association with the junction into cooperation with the second half link. This half link is to all intents and i purposes identical with the connector side of the ordinary link, certain features which are not required being omitted, for example, relay RE which is only required in connection with re-ringing a calling party is not included in the second half link as it will never be required. The relays in thishalf link may be distinguished from those of 1 the connector side of the ordinary link by virtue of the fact that they are designated IB, IBA, IC, etc., their functions however being identical with those of the relays B, BA, C already described. If this additional half link is in use on an incoming main exchange call and the ordinary link is freed, there will be no interference with the main exchange call since relays CA, CB and CC remain held over lead 33 from armature H13 in the additional half link.

In case it is desired to give a discriminative signal when a coin box "subscriber originates a call, this may be effected by arranging to operate a relay over an additional finder bank and wiper, this relay upon operating causing a distinctive ringing signal to be extended over the junction. The necessary discrimination could be effected by-applying normal ringing current to the juncr tion when an ordinary subscriber calls and applying ringing current via a half wave rectifier to the junction when a coin box subscriber calls.

In areas of the type described, it will be appreciated that it is very desirable to be able to per- ,5- form a centralised testing of all subscribers lines the various exchanges from the main exchange and arrangements are made whereby'a test clerk may set up a connection to a subscribers line in the normal manner and may then by applying L03 to the junction a high potential pulse of reverse polarity to that required for verification release purposes bring about the removal of all trans-- mission bridges from across the speaking leads and the by passing of the bridge condensers so 551 as to give a through metallic loop. On the reception of such a pulse at the tandem-R. C. X.-

a-fter a connection has been set up to a line connected to the tandem R. C. X. the neon tube NL, Fig. 6, strikes and the resulting current flow 30; will be in a direction to which rectifier MBA is conductive and hence relay TC now operates.-

This relay at armature tcl, Fig. 2, operates relay TS which at armature tsl prepares acircuit for relay SW. I

55 At the end of the high voltage pulse, relay TC restores and a circuit is then completed for relay SW in series with relay TS which remains held.

Thereupon at armatures $1113 and sw4, Fig.7, re-' lays A and 0C are disconnected from the juncmg tion and the bridge condensers QD and QC are sh'ort-circuited. A local holding circuit is com--v pleted for relay A over armature m2 and resist.- ance YK so as to maintain the connection while. relays CI and CD are disconnected at armatures sw5 andswl.

Thetest clerk is now in direct metallic connection with the desired subscribers line, and since relays F and H Will have been already operatedon the reply of the subscriber, the only apparatus connected to the line at the R. C. X. 5 is the neon tube NL and its associated responding relays. Since however this tube in its normal condition. offers substantially infinite resistance, its effect on the testing of the line may be neglected.

On the completion of the testing, the test clerk causes thesame high voltage potential to be reapplied tothe junction in order to restore the common equipment to its original condition.

Again relay TC is operated thereby releasing relay TS but holding relay SW over its lower winding and armature sw'l. At the end of the pulse, relay SW releases also and relay A in the common equipment is re-connected to the junction. The

connection. may subsequently be released in the 0 usual way by disconnecting the loop to relay A whereupon the R. C. X. equipment is freed for i use on further calls.

In case the line to be tested is connected to the adjacent R. C. X., relay SRB is operated over 3 tures srbl and srbZ short-circuits condensers QC and QD immediately so as to relay the high voltage pulse to the adjacent R. C. X. and at armature srb3 holds relay A. On the operation of relay SW when the pulse ceases, relay SRB is released at armature sw6. is received for restoring conditions to normal, relay TC again operates and releases relay TS while holding relay SW. The pulse is therefore relayed-to the adjacent R. C. X. and relay SRB cannot now operate as its circuit is opened at armature sw6. At the end of the pulse relays 7 TC and SW release and conditions are restored to normal.

The rectifiers MRC and MRD in circuit with relay A serve to prevent a high voltage pulse from circulating through the exchange battery via its windings in series. In case it is desired to check the correct functioning of the R. C. X. board from the main exchange, the operator dials a so-called test num ber whereupon the connector side of the link is set into association with the test number relays TT and TN in the equipment of Fig. 11. Relay TN is thereupon operated over the P lead in series with relay H and the lefthand winding of" the retard TT serves to trip the ringing and so operate relayF. The operator will now be connected through. Relay TN at atmatures m2 andtn-S starts up the busy tone and ringing equipments .by earthing leads Ill and I3 respectively. Hence if the equipment is working correctly the operator will receive a continuous tone at the frequency of the ordinary busy tone which is extended from the transformer TI and viaarmatures fa3 and ml to the right hand winding of retard TT whence it is extended by induction over the line to the operator. In case a fuse should be blown, relay FA will be operated as already described and at armature m3 it connects up the ringing tone transformer T2 in place of the busy tone transformer TI. The operator willtherefore receive an inverted ringing tone, that is to say, the ordinary on and off periods are reversed since the connection is made via the back contact of armature iraZ. The operator isthus 7 When a further pulse 351 informed as to the condition of the equipment and this facility is particularly useful in the case of unattended boards.

The relay TH which is very slow to operate and may be of the thermostat or dash pot type comes into action if the finder switch is set in operation and owing to some defect fails to find the calling line. Thereupon at armature thi relay FS is disconnected but remains held over its lower winding. When the operator plugs in she will find no one on the line and will attempt to ringthe calling party. This will be impossible owing to the non-operation of relay FF and When the operator removes her plug relays BA, FS and TH will all release. If the calling line is common battery operated, a call will again come in and the procedure will be repeated assuming thelfault has not cleared itself automatically. The operator will then realize that there is trouble at the tandem R. C. X. and will take steps to have it dealt with.

We claim:

1. In a telephone system including a plurality of exchanges, means including a trunk line for interconnecting said exchanges in tandem, a source of high voltageat one of said exchanges, means for connecting said source to said trunk line, a relay and a gas discharge tube connected in series at another of said exchanges operated in response to the connection of said high voltage .source to said trunk line, feeding bridges and transmission condensers in said other exchange normally effective for completing the talking circuits for established connections in the said other exchange, and means operative in response to the operation of said relay for cutting outsaid feed ing bridges and said transmission condensers and for extending said high voltage source over the connection to a further exchange to eifect a switching operation thereat.

2. In a telephone system including a plurality of exchanges, lines terminating in one of said exchanges, a trunk line extending from'said one exchange and terminating in an operators position at another of said exchanges, a calling line and means for automatically connecting said calling line to said operators position by way of said trunk line, automatic switches in said one exchange controlled over said trunk line from said operators position for setting up connections to said lines, feeding bridges and transmission condensers at said one exchange normally included in the connections established to line in said one exchange, testing means at said operators posi- .1 tion for permitting the operator to test the connected lines in said one exchange over said trunk line, said testing means including means for connecting a pulse of high voltage to said trunk line,

a relay and a gas discharge tube connected in series in said one exchange, said relay and gas tube being unresponsive to normal current flow in an established connection but responsive to said pulse of high voltage to cause operation of said relay, and means controlled by the operation of said relay for cutting out said feeding bridges and condensers to establish a metallic loop between the operators position and the connected line for testing purposes.

3. In a telephone system, a plurality of exchanges, a control exchange connected in tandem with said plurality of exchanges, an operators position in the control exchange, lines terminating in said plurality of exchanges, means including said operators position for establishing a connection to a called one of said lines in any one of said connected exchanges, feeding bridges and transmission condensers providing the talking circuits included in said established connece tion, means at said operators position for tr'ansa mitting a high voltage signal of one polarity or the opposite polarity to said established connection, relay means and a gas discharge tube con nected in series included in said established con-v nection, said relay means and said gas discharge tube being unresponsive to normal current flow but responsive to said high voltage signal to causethe operation of said relay means, and means controlled. by the operation of said relay means for cutting out feeding bridges and said transmission condensers in said established connection or for releasing said established connection dependent upon the polarity of said high voltage signal transmitted to said connection.

4. In a telephone system, a plurality of -ex-. changes, an operators position in one of said ex-a changes, lines terminating in the other exchanges, means responsive to the initiation of a call from a line in any one of said exchanges for automatically connecting said calling line to said operators position, numerical switches in the exchange terminating said calling line operated by the operator over said original connection to extend a verification connection to the calling line to verify the number given by the calling party as his own, meansfor transmitting a high relay and a gas discharge tube connected inseries included in said original connection, said relay and gas discharge tube being unresponsive .to normal current flow but responsive to said high voltage signal to cause the operation of said relay, and means controlled by the operation of said relay for releasing only said numerical switches included in the verification connection without releasing said original connection whereby said numerical switches may be used to set up a connection to a called line.

5. In a telephone system, a first and second mission condensers associated with said control.

and switching apparatus and normally effective for completing the talking circuits for established connections between said lines, a source of high voltage at the first exchange, means for connecting said source to said one line interconnecttube connected in series in said control and. switching apparatus, said relay and said tubebeing normally ineffective to normal currentqflow but effective in response to the connection of said' source to said one line to operate said relay, and means controlled by the operation of said relay .3( voltage signal over said original connection, a

' ing said exchanges, a relay and a gas discharge for cutting out said feeding bridges and said transmission condensers. 6. In a telephone system, a plurality of exchanges, a control exchange connected in tandem with said plurality of exchanges, an oper-- ators position in the control exchange, lines ter-' minating in said plurality of exchanges, means. including said operators position for establish-' ing connections between said lines in any of said connected exchanges, feeding bridges and trans mission condensers providing the talking circuits included in said established connections, means at said operators position for transmitting a high.

I 2,207,633 voltage signal of one polarity or the opposite polarity to an established connection to any one of said lines, a first. relay and a gas discharge tube connected in series included'in said connection being unresponsive to normal current 'flow but responsive only to said high voltage signal of said one polarity to cause the operation oi said first relay, means controlled by the operation of said first relay for cutting out said feeding bridges and transmission condensers, a second relay and. said gas discharge tube connected in series included in said connection being unresponsive to normal current flow but responsive onlyto high voltage signal of said opposite polarity to cause operation of said second relay,

means for transmitting impulses iromthe first exchange over said trunk line to said repeater, a feeding bridge and transmission condensers associated with said repeater, said feeding bridge responsive to said transmitted impulses for repeating said impulses, means associated with said repeater responsive to said'repeated impulses for extending the connection, .a gas discharge tube normally connected across the speaking leads of said repeater, means operative only during the repeating operation for disconneting said tube to prevent the striking of said tube in response to inductive surges created during the impulsing operation, means for transmitting a high voltage signal from said first exchange over said trunk line to said repeater to cause said tube to strike, and means operated in response to the striking of said tube for cutting out said feeding bridge and for short-circuiting said transmission condensers.

8. In a telephone system as claimed in claim 1 including means whereby the second connection of said high voltage source to said trunk line causes the re-insertion of said feeding bridges and transmission condensers.

9. In a telephone system as claimed in claim including a test clerks position in said first exchange and means for testing a line in the second exchange from said position effective in re-- sponse to cutting out said feeding bridges and transmission condensers.

l0. In a telephone system as claimed in claim 4 including means whereby themeans for releasing said verification connection persists only as long as said high voltage signal is applied to said original connection.

relays is operated in accordance with the polarity of said high voltage signal.

12. In a telephone system as claimed in claim 4 including means at the operator's position for transmitting a signal by grounding both speaking leads of the original connection to the operator, and means responsive to this signal for connecting a busy called line to the operators position.

13. In a telephone system as claimed in claim 5 including means for temporarily disconnecting said gas discharge tube to prevent the striking of gas discharge tube by the inductive surges produced'during the a called line.

14. in a telephone system, a distant exchange, a tandem exchange, a trunk line interconnecting said distant and tandem exchanges, a main exextension of a connection to change, an operators position at the main ex- 7 change, a control trunk extending from said 130-.

sition to said tandem exchange, subscribers lines terminating in said distant andtandem exchanges, means responsive to the initiation of a call by a calling line insaid distant exchange for automatically extendinganoriginal connection from the calling line by way of said trunk line, said .tandem exchange, and said control trunk to said operators position, a numerical switch in said tandem exchange, a second numerical switch in said distant exchange, means controlled by the operator in case the operator desires to verify the number of said calling line for directively operating the numerical switch in the tandem exchange over said control trunk to connect with said trunk line interconnecting the distant and tandem exchanges and for then directively operating said second nurnerical switch in the distant exchange over said control trunk, said first numericalv switch, and said trunk line to connect' with said calling line to verify the number given by the calling party, means thereafter controlled by the operator over said control trunk for releasing said first and second numerical switches while maintaining saidoriginal connection, said release of said numerical switches thereafter enabling said operator to directively control one of said switches or both of said switches to extend a connection to a called line in said tandem or dis tant exchanges to connect the calling and called extending'from said position to said distant exchange, means responsive to the initiation of a call by a calling line in said distant exchange for automatically extending anoriginal connection" from the calling line by way of said controltrunk to said operators position, a numerical switch in said distant exchange, means controlled by the operator in case the operator desires to verify the number of said calling line for directively operating said numerical switch over said control trunk to connect with said calling line to verify the number given by the calling party, means thereafter controlled by the operatorover said control trunk for releasingsaid numerical switch while maintaining said original connection to the calling line, said release of said numerical switch thereafter enabling said operator to directively control said numerical switch to extend a connection over one of said toll trunks to establish 

